But let me also tell you this: I don't want to sound discouraging, but I think you're trying to chew on a bone that's too big for you.
Do-it-yourself is great, up to a point. Beyond that point you need a professional.

If you have a hole in your tooth, do you fill it yourself or go to the dentist?

Hire a foundation contractor/deck builder, offer to help him for reduced price and learn from watching him. Trust me, it will cost you less.

But let me also tell you this: I don't want to sound discouraging, but I think you're trying to chew on a bone that's too big for you.
Do-it-yourself is great, up to a point. Beyond that point you need a professional.

If you have a hole in your tooth, do you fill it yourself or go to the dentist?

Hire a foundation contractor/deck builder, offer to help him for reduced price and learn from watching him. Trust me, it will cost you less.

Understand, but a) the original builder did not do it correctly and b) another local professional I hired recently also did not use the better techniques. He figured using "cedar" would negate poor flashing. In the very least, I will use my knowledge to select a "pro".

TOH, other websites, etc are a great source of info. The stick-on membranes, etc appear to be a newer technology than some around here have kept up with. I could mention that the house itself is not house-wrapped. From what I see, it goes framing, OSB, siding. Not even good old tar paper. I suppose a covered porch will protect against water pretty well on its own. On the half I have torn apart, the siding looks ok where the ledger was direct screwed with 3" screws -- about 3 screws every two feet -- yes, just regular old screws, and yes, 3" (so figure 1.5" for the ledger, and another 1" for siding and osb, that means my ledger had all of 1/2" of the screw in the rim joist. The siding is painted under there, so not sure if the original builder gets the "credit" for this work, or someone else. I know it was not the original owner. In any event, I'm feeling pretty confident I can do better than that. I do appreciate the frankness of your reply. I hope mine does not inhibit you our others from giving me some feedback.

Understand, but a) the original builder did not do it correctly and b) another local professional I hired recently also did not use the better techniques. He figured using "cedar" would negate poor flashing. In the very least, I will use my knowledge to select a "pro".

TOH, other websites, etc are a great source of info. The stick-on membranes, etc appear to be a newer technology than some around here have kept up with. I could mention that the house itself is not house-wrapped. From what I see, it goes framing, OSB, siding. Not even good old tar paper. I suppose a covered porch will protect against water pretty well on its own. On the half I have torn apart, the siding looks ok where the ledger was direct screwed with 3" screws -- about 3 screws every two feet -- yes, just regular old screws, and yes, 3" (so figure 1.5" for the ledger, and another 1" for siding and osb, that means my ledger had all of 1/2" of the screw in the rim joist. The siding is painted under there, so not sure if the original builder gets the "credit" for this work, or someone else. I know it was not the original owner. In any event, I'm feeling pretty confident I can do better than that. I do appreciate the frankness of your reply. I hope mine does not inhibit you our others from giving me some feedback.

I understand that you are determined to do it yourself.
I understand that you are fed up with the builder and one contractor.
But:
We are volunteers here and can give hints here and there, we are not a construction school. You can learn more from the videos.

Now to your problem: If your house doesn't have Tyvek or similar, you will have to make sure that water doesn't get in between the house and the ledger somehow. Install an L shape metal across on the top of the ledger to cover the membrane as well. When you secure it to the wall, put a bead of tar behind the metal to stop water from going between the membrane/ledger and the house.

Ever heard the term "water off a ducks back"? Apply that to keeping water off the rim joist of the house and you will be OK. This means that a drop of water will flow from one surface to another through a shedding process, that is it never hits a crack or crevice. If it does, caulk, weatherstripping or waterproofing materials will eventually fail and water will get in.

Apply flashing so that water is always being directed down and away from the house. As for the spacers to the ledger boards, I don't like those. It weakens the structure. Remember, you are building a porch, not a deck. You have a roof over the porch and that will keep a lot of water away from the foundation.

BTW, you cannot use screws to attach the ledger, you must use bolts. 1/4" lag bolts are commonly used but I like the FastenMaster HeadLok fasteners for this. They really have a lot of holding power, you need at least the 4.5" but if you have a double rim joist like I do, you might want to go with a 5.5" or 6" length.

-remove siding at least 6" above ledger location on wall; this will expose the OSB
-apply stick-on waterproof membrane from that point to the bottom of osb
- attach ledger with 1/2" lag (2 on each end, 1 every 16") or equivalent "bolts"
- I plan to use 2x8" PT for the ledger
- apply metal L (with drip edge) flashing to fit atop the ledger extending up the wall a few inches, then out over and down the ledger itself
- apply stick-on membrane over metal flashing

That should direct any water from above down, out, and over the ledger. As one stated - the covered porch is my biggest ally here. Given I'm not well flashed and waterproofed to this point, this should be adequate. The existing siding/osb show now signs of water damage - though ALL the conditions were idea for damage to occur.

1/2" lag bolts are a bit too big, I think that was a type in the link you posted. 1/4" lag bolts with a large washer will work fine, but I really like the fasteners I linked to. The threads are roll formed wich makes them protrude from the shaft for a better grip. They have a nice wide head so you don't need a washer. They are pricy though, but I think they are worth it. You aren't using that many in the long run.

1/2" lag bolts are a bit too big, I think that was a type in the link you posted. 1/4" lag bolts with a large washer will work fine, but I really like the fasteners I linked to. The threads are roll formed wich makes them protrude from the shaft for a better grip. They have a nice wide head so you don't need a washer. They are pricy though, but I think they are worth it. You aren't using that many in the long run.

I have 1.5" ledger, the 1.5" house rim, and figure another 1/2" in osb, so 4" should be long enough.

This --https://www.decks.com/deckbuilding/Ledger_Board_Fasteners -- suggests a pair, one atop the other, near the ledger ends, and then alternating one at the top, next at the bottom 36" OC since my joists will run about 6' from ledger to concrete pier. I'll probably go 24-30" for good measure. If I use lag bolts, Google seems to still suggest 1/2" , or maybe 3/8", but they require pilot holes. So at 30" spacing, "headlok" looks real appealing.

Yep, those are the ones I used, but i paid more than that for them, about $16 for a dozen. I used the pattern in your second link but I spaced them a little closer. I also used a pair of 16d nails on 16" centers to keep the ledger board tight to the rim joist, just in case it wanted to twist on me.

The nails keep it flat, the headloc bolts keep the ledger from pulling away from the wall. BTW, the headloc fastener was developed because of decks that pulled away from the structure they were attached to, sometimes with fatal results. Nails alone will not keep the ledger attached and sometimes lag bolts don't work as well as people think, especially zinc coated lag bolts.